Manganese alloys



Patented .inne 26, 1345 MANGANESE ALLOYS Reginald S. Dean,

sait Las@ city, Utah., assigner to Chicago Development Company, Chicago,Ill., a corporation o1 Illinois 13 Claims.

My invention relates to the preparation and heat treatment o; alloysconsisting essentially of manganese, iron and chromium, and isparticularly concerned with the preparation of such alloys which arehighly resistant to atmospheric corrosion, possess the ability towithstand great extension by cold work without the hardening which ischaracteristic of austenitic stainless steels and irons heretofore knownin the art, and, in addition, have the properties of retainingworkhardening at relatively high temperatures, oi

hardening and being rendered non-magnetic,

Without embrittlement, by heat treatment.

Alloys ofv manganese, chromium and iron have heretofore been suggestedbut, in all cases, those alloys whose properties have been investigatedhave contained asubstantial content of carbon,-

of the order of 1% or more, although suggestions have been made foralloys where the carbon content was allegedly zero. In such alloys oftheprior Cri art, the manganese content always was lessthan that of thechromium. Such alloys are disclosed by the prior art to have a magneticpermeability not exceeding from 2 to 5% of that of cast iron. In otherknown alloys containing manganese, chromium and iron, present, thesilicon and up to 8%.

The alloys of my invention are sharply distin guishable from those ofthe prior artl not only in composition but in physical characteristicsand properties, including amenability to different types of heattreatment. Thus, for example, the alloys of my invention must besubstantially free from the oxides of silicon and aluminum, carboncomprising in excess of 3% both carbon and silicon are issubstantially,- and preferably entirely, absent,

and silicon should not exceed 1 and is preferably present in amountsless than 0.7% and particularly close to 0%. In connection with thematter of properties of the alloys of my invention, it may be pointedout, among other things, that their magnetic permeability, afterquenching from high temperatures, is substantially that of cast iron, aproperty which distinguishesthem radically from numeroiis of the alloysof the prior art. As is well known and shown in Handbook for ElectricalEngineers, by Harold Pender, first edition, published by John Wiley 8:Sons, Inc., New Y'ork City (page 901B),4 cast ironr at a eld strength of100 ampere turns per inch has a permeability of from or from about 1.35,to ,1.5m The alloys of my es invention, therefore, have a permeabilityfalling within this same general range.

Again, there is a denite and radical. dierence between the heattreatment proposed by the prior art as applied to alloys of manganese,chromium and iron and the heat treatments which I utilize. The heattreatment of the alloys of the present invention usually consists of aquenching, cold working and reheating procedure, the quenching takingplace from a temperature higher than 1100 degrees C. and particularlyabout 1200 degrees C. The heat treatment described'in thev prior artwith respect to manganese, iron, chromium alloys involves heating thecast alloy to 1000 degrees C. to 1100 degrees C. for several hours andthen cool ing in the furnace. Such a heat treatment does not produceincreased strength in the allo'ys of my invention. Here it has nosubstantial edect on the hardness or produces a softening, dependingupon the rate at which the alloys were cooled in casting. Heating thealloys of my present invention to 1000 degrees C. causes softeningwithout the reappearance oi magnetism, that is, they are not carriedinto the state from which they were quenched. This state is onlyattained at higher temperatures, usually above 1100 degrees C.

It will be seen, therefore, as hereinafter pointed out in detail. that,by a suitable selection of alloy composition and by heating of thealloys to a proximately 1200 degrees C and quenching, I may cold workthe said alloys by rolling, swaging or by any other means to an extent,in many instances, of 90% or more reduction in area without excessivehardening. By excessive hardening, I refer to l any hardness laboveabout 25 as measured on the Rockwell C scale. I have found that therange of alloy composition in which this phase of my invention may bepracticsed may be dened approximately as follows: If the said alloyscontain at least 18% ganese is substantially entirely free of carbon andoxides of silicon and aluminum and egceeds the amount of chromium, acertain critical amount of chromium must be present to prevent excessivehardening of the alloys by cold working. This critical amount ofchromium depends on the manganese content of the alloy. Between 18% and30% manganese. where the manganese exceeds the chromium, the criticalminimum percentage of chromium is 17.5% and-the upper percentage ofchromium is about 19%. Above 30% manganese, the critical minimumpercentage of chromium falls, being 12.5% when the manganese is 40%, theupper percentage of chromium in such case being about. 16%. In the rangeof 10% manganese, and wherein the mam.

Rlockglell O ar ess Pell-ent cold worked 75% reduc tion in area Per centPer cent Mn Cr All of the alloys in the range of composition set outhereinabove, as previously indicated. have a magnetic permeability ofthe same order as that of cast iron.

The alloys within the composition range which I have set forthhereinabove, as previously stated, may be greatly hardened andstrengthened by heat treatment after quenching from about 1200 degreesC.4 and c old working. I have found, for example, that alloys having atleast 18% manganese and at least the critical amount of chromiumnecessary for great extension by cold work without undue hardening butcontaining less than the uppercritical-limit of chromium may be hardenedwithout-embrittlement by heating to temperatures between about 400degrees C. and about 800 degrees C. after quenching from approximately1200 degreesC. and cold working. Within the percentage ranges set outhereinabove, the range or variation in the limiting percentage ofchromium is` substantially linear. While the amount of hardening whichis obtainable in the alloys of my invention varies somewhat with thetemperature of heat treatment, the important factor is, however, that,by the practice of my invention, Yhardeningimay be obtained withoutembrittlement. This is in sharp contrast from the results obtained withalloys of iron, manganese and chromium heretofore known in the art, allof which, due to the presence of oxides of aluminum or silicon or tocarbon or to the selection of relativeproportions of iron, manganese andchromium, become brittle at room temperatures after being heated totemperatures of about 600Hdegrees C. after quenching from'about 1200degrees C. followed by cold working. For the purpose of illustratingthis phase of myv invention, the

While there is a small amount of hardening Abelow the criticalpercentage of chromium, the

rangeV of hardening is,.however, materially less than above the criticalpercentageof chromium for best coldworking, accordingly, I preferparticularly to utilize those alloyshaving more than the critical amountof chromium in the practice of the preferred aspects of my invention. Inceriron become brittle by reheating at any temperal tain cases, someuseful results may be obtained with not more than 2.5% less than thecritical amount of chromium as hereinabove dened.

It should be understood that the hardness of the alloys, after reheatingto about 600 degrees C., is not necessarily the maximum hardness whichcan be obtained. Haldening at this temperature is described for thepurpose of illustrating the fact that the alloys of my present inventiondo not become brittle on heat treatment, since I have found that, ifalloys of manganese, chromium and ture, they do so at about 600 degreesC. It is not uncommon, fo-r example, to obtain hardnesses as high asabout Rockwell C 60 by heating at ternperatures somewhat below 600degrees C. It should be understood that I consider an alloy brittle whenit will not give a reading on the Rockwell C scale without chipping. Ihave found this to be a reliable indication of the extent of brittlenesswhich renders an alloy useless or substantially so for at least mostcommercial purposes.

The alloys of my invention, while hardening less by cold work thanaustenitic alloys of iron, chromium and manganese; retain or enhancetheir hardness by heating to temperatures such as 800 degrees C., atreatment which softens the austenitic alloys of iron, chromium andmanganese. This is illustrated by the following examples:

Illustrative alloy of present invention Austenitic alloy Mnl-25,; Cr-lS;Fe-57 Cold worked, 20 Rockwell C 650 C., 5l Rockwell C 800 C., 45Rockwell C Mil-25; Cr-lO; Fe-65 Cold worked, 39 Rockwell C 650 C., 20Rockwell C 800 C., 2 Rockwell C Alloys falling within the scope of myinvention, if anealed, for example, at about 800 degrees C. or even ashigh as 1200 degrees C. and slow cooled, are' much harder and strongerand much less workable than austenitic iron, chromium.V and manganesealloys. When heated to temperatures from 1000 degrees C. to 1200 degreesC. and rapidlyv cooled, however, the forged or otherwise worked alloysof my invention are softened, and when quenched from 1200 degrees C.they have certain properties comparable to nickel silver and austenitic.iron, chromium, manganese. alloys in the annealed state. This isillustrated by the following examples:

Illustrative alloy of present invention [Mn-25; Cr-ls; Fe-:m

tained if it were allowed to cool in an ordinary y heat-treatingfurnace; in general,.by cooling at a rate such that at least six hoursis required for the alloy to reach room temperature after the heat isturned off. It will be understood, of course, that the length of timerequired to bring the temperature of the heated alloy down to roomtemperature during the slow cooling process will depend, in part, uponthe size and shape of the alloy element being treated. It will also beunderstood that the slow cooling may be carried out in airalthough, forbest results, it' should be carried out in an inert atmosphere. Thealloys which have this property contain from 22% to 30% manganese, from15% to about 30% chromium, balance iron, the manganese not being lessthan the chromium and, particularly, exceeding the chromium.

As I have previously indicated, alloys of the present invention whichcontain from 22% to 30% manganese and more than 19% chromium cannot behardened at 600 degrees C. after quenching from 1200 degrees C. withoutembrittlement. Hence, the alloys of myinvention which may be hardenedwithout embrittlement by either 1) slow cooling or (2) by quenching andreheating are those containing approximately 25% manganese,approximately 18% chromium, and balance substantially all iron.

With respect tomagnetic properties, I have found that the alloys whichare hardened after quenching and cold work without becoming brittle at600 degrees C. lose a substantial proportion of their magnetism. Theymay, however, harden usefully without losing their magnetism.

I have found a wider range of alloy compositions which possess usefulhardening characteristics below 600 degrees C. but which become brittleat that temperature. This group of alloys embraces all of those abovethe critical percentage of chromium necessary to prevent undue harden-[All alloys quenched from 1200 C. and cold worked] Per cent Per cent Percent Hardness Hardness Mn Cr Fe cold worked 550 Q 25 23 52 24 s4 25 20,55 43 25 25 5o 25 io In the practice of my invention, I prefer to employelectrolytic manganese having a purity of at least about 99.0% andpreferably of 99.9%.

By virtue of their hardening by reheating after quenching, particularlywith intermediate cold work, my alloys are particularly useful forvarious purposes as, for example, gears, bearings, armour plate, and forpurposes, in general, where case-hardened nickel or nickel-chromiumsteels have heretofore been used. The alloys of my present invention,hardened as described herein, have a wide utility in articles ofcutleryl ball and roller bearings, tools and dies, especially saws, andother tools which are necessarily exposed to corrosive iniluences. Inthe soft state, the alloys of :my present invention maybe employed forcooking utensils and other purposes where a relatively soft material ofsatisfactory working qualities and a high degree of stainlessness isdesired. They may also be utilized in the aircraft andl automotiveindustries such as for the manufacture of thin sheets, of very highstrength, for the fabrication of airplane wings or the like.

My presentapplication is a continuation-inpart of my copendingapplications Serial No. 219,501, led July 16, 1938, now Patent No.2,286,-

199, issued June 16, 1942; and Serial No. 267,706,

cent up to 25 per cent manganese and from 12 per cent to 15 per cent at40 per cent manganese with intermediate chromium percentages atintermediate contents of manganese in said alloys, the manganese beingnot less than the chromium, the balance being substantially all iron,said alloys being severely cold worked and having magnetic permeabilityof about 1.35,:1. to 1.57/1 Vat a v eld strength of 100 ampere turns'perinch and being capable of retaining or enhancing their hardness whenheated toV temperatures from about 800 degrees C. to about 1200 degreesC, and slow cooled and of softening by heating to temperatures between1000 degrees C. to 1200 degrees C, followed by rapid cooling.

2. Alloys consisting of substantially only iron,

l manganese and chromium, substantially free from' carbon and fromoxides of silicon and alu..

mium, said alloys being cold Worked to a high degree after quenchingfrom about 12:00 degrees C., said alloys having a magnetic permeabilityof about 1.35# to 1.571 at a field strength of 100 ampere turns perinch, said alloys containing morethan 18 per cent and less than 45 percent manganese and a percentage of chromium from ploy electrolytic iron,electrolytic chromium and electrolytic manganese of high purity so asnot to introduce deleterious constituents into the alloys. I have found,for example, that the presence of oxides of aluminum and silicon, suchas are present in silica-thermic or aluminothermic manganese orferro-manganese prevents the effective practice of my invention. Whilethe mnatmese whiieI employ may/be produced by a vacuum 17 per cent to 32per cent where the manganese content of said alloys is up to 25 percent, and

r from 12 per cent to 15 per cent chromium at 40 Der cent manganese,with intermediate percentages of chromium at intermediate contents ofY lmanganese, the manganese being always in excess of the chromium, thebalance being substantially all iron. l

3. Hardened alloys consisting of substantially only iron, manganese andchromium, substantially free from carbon and from oxides of siliheatingthe same to a temperature of about 400 distinction process, I prefer,particularly. to em- ,76 decrees C. toabout 800 degrees C. afterquenchcent to per cent chromium at 40 per cent manganese, withintermediate percentages of chroinium at intermediate contents ofmanganese, the manganese being always in excess of the chromium, thebalance being substantially all iron.

4. Alloys consisting substantially onlyof iron,

vmanganese and chromium. substantially free from carbon and from oxidesof aluminum and silicon, said alloys having more than 18 per cent andless than 45 per cent manganese and a percentage of chromium from 17percent to 32 per cent up to 25 per cent manganese and from 12 to 15 percent at 40 per cent manganese with intermediate chromium percentages atintermediate contents of manganese in said alloys, the manganese beingnot less than the chromium, the balance being substantially all iron,said alloys being severely cold worked and having magnetic permeabilityof about 1.35# to 1.57# at a field strength of 100 ampere turns perinch, said alloys being in a softened condition by reason of beingheated to temperatures between about 1000 degrees C. and about 1200degrees C followed by rapid cooling.

5. Alloys consisting of substantially only iron, manganese and chromium,substantially free from carbon and from oxides of silicon and aluminum,said alloys being worked to a high degree after quenching from about1200 degrees C.,

said alloys having a magnetic permeability of about 1.35a to 1.57/1 at aeld strength of 100 ampere turns per inch, said alloys containing morethan 18 per cent and less than 45 per cent manganese and a percentage ofchromium from 17 per cent to 24 per cent where the manganese content isup to 25 per cent, and varying substantially linearly to about 15y percent chromium at 40 per cent manganese, the manganese being always notless than the chromium, the balance being substantially all iron, saidalloys having the property of not becoming brittle atroom temperatureafter heating to any temperature belowl their melting points followed byslow cooling.

6. Alloys consisting substantially only of iro'n, manganese andchromium, substantially free from carbon and from oxides ofaluminum andsilicon, said alloys having more than 18 per cent and less than 45 percent manganese and a percentage of chromium from 17 per cent to 24 percent where the manganese content is up to 25 per cent and varyingsubstantially linearly to about 15 per cent chromium at 40 per centmanganese, the manganese being always not less than the chromium, thebalance being substantially all iron, said alloys having magneticpermeability of about 1.35/1 t0 1.571. at a eld strength of 100 ampereturns per inch and being hardened by reason of having been quenched fromabout 1200 degrees C. followed by cold working and reheating totemperatures between about 400 degrees C. and about 800 degrees C.

7. An alloy consisting essentially of approximately 25 per centmanganese, approximately 18 per cent chromium and the balancesubstantially all iron, said alloy being substantially free from theoxides of aluminum vand silicon, said alloy being hardened withoutembrittlement by quenching from approximately 1200 degrees C., coldworking and reheating to a temperature between about 400 degrees andabout 800 degrees C.

8. An alloy containing approximately 25 per cent manganese,approximately 18 per cent chromium and the balance substantially alliron, said alloy being substantially free from the oxides of aluminumand silicon, said alloy being hardened by slow cooling fromapproximately 1200 degrees C.

9. An alloy containing approximately 37 per cent manganese,approximately 14.5 per cent chromium and the balance substantially alliron, said alloy being substantially free from the oxides of aluminumand silicon, said alloy being hardened without embrittlement byquenching from approximately 1200 degrees C., cold working, andreheating to a temperature between about 400 degrees C. and about 800degrees C.

10. vA .magnetic alloy capable of being cold worked to a high degreewithout exceeding Rockwell C 25, of being hardened without embrittling,

having the property of suffering loss of magnetism either by slowcooling from 1200 degrees C. or by quenching from 1200 degrees C. andreheating to 650 degrees C., and having a composition from 23 to 28 percent manganese, from 17 to 19 per cent chromium, balance beingsubstantially all iron.

11. A hardened non-brittle alloy resulting from I slow cooling of saidalloy fromA temperatures of about 1200 degrees C., said alloy containing22 to 30 per cent manganese, 15 to 30 per cent chromium, the manganesenot being less than the chromium, balance substantially all iron.

1.2. Stainless alloys hardenable without cracking by heating, cooling,and reheating to a. lower temperature, said stainless alloys which areductile as cast consisting essentially of chromium,

manganese, and iron in the following proportions: 14% to 16% chromium,36% to 39% manganese, and the balance iron, with the exception of suchsmall amounts of impurities as will not affect the properties of thealloys.

the alloys.

REGINALD S. DEAN.

